1. Field of the Invention
The present invention relates to a magnetic tape cartridge, in which a single tape reel with magnetic tape wound thereon is rotatably housed within a cartridge case and a tape leader pin is coupled with the leading end portion of the magnetic tape.
2. Description of the Related Art
In the magnetic tape cartridges, which are used as storage medium to be employed in external storage units for computers, etc., there is known a type where a single tape reel with magnetic tape wound thereon is rotatably housed within a cartridge case. This magnetic tape is employed as a data archiving tape for computers, etc., and stores important information. For this reason, the magnetic tape cartridge is constructed so that trouble, such as tape jamming, etc., does not occur and that the magnetic tape is not pulled out from the cartridge case unexpectedly.
Also, a tape leader pin is coupled to the leading end of the magnetic tape. When this magnetic tape cartridge is loaded into a recording-reproducing unit, a pin catching member on the side of the recording-reproducing unit engages the tape leader pin and pulls out the magnetic tape from the cartridge case. On the other hand, when the magnetic tape cartridge is unloaded from the recording-reproducing unit, the magnetic tape is wound on the reel and the tape leader pin is returned into the cartridge case by the pin catching member. The tape leader pin is detachably retained in a predetermined position, by a pin retaining spring member provided within said cartridge case so that it faces the tape leader opening of the cartridge case.
The aforementioned tape leader pin is illustrated in FIG. 1A. This tape leader pin P and magnetic tape T are coupled with each other, as illustrated in FIG. 1B. The tape leader pin P is constructed of a pin main body 5 and a clamp member 6, as disclosed in Japanese Unexamined Patent Publication No. 11(1999)-232826. The pin main body 5 is formed, for example, from stainless steel and consists of a tape clamp portion 5a interposed between a pair of inner flange portions 5b, small-diameter portions 5c formed outside the inner flange portions 5b, and outer flange portions 5d formed outside the small-diameter portions 5c. The clamp member 6 is formed, for example, from synthetic resin. This clamp member 6 is equipped with an axial slit 6a and has a C-shaped cross section. The clamp member 6 is inserted elastically on the tape clamp portion 5a of the pin main body 5, and magnetic tape T is clamped between the clamp member 6 and the tape clamp portion 5a. 
FIG. 2 illustrates a conventional magnetic tape cartridge disclosed in Japanese Unexamined Patent Publication No. 2000-36179. Note that in FIG. 2, the right side in the figure is the front side of the cartridge case, because the cartridge case is inserted toward the right side when it is loaded into a recording-reproducing unit.
In this magnetic tape cartridge, a single tape reel (not shown) with magnetic tape T coupled at its leading end with a tape leader pin P is rotatably housed within a cartridge case 4 consisting of an upper case (not shown) and a lower case 3 fastened together by means of small bolts, etc. A tape leader opening 10 for leading the magnetic tape T is formed in one side wall of the cartridge case 4. This tape leader opening 10 is constructed so that it is opened and closed by a slide door (not shown) urged in a closing direction with a spring member (not shown).
The tape leader pin P, coupled with the leading end of the magnetic tape T, and having construction such as that shown in FIG. 1, is inserted in and out of the magnetic cartridge through the tape leader opening 10. The top and bottom walls inside the tape leader opening 10 are provided with pin housing recesses 45 into which the upper and lower flange portions 5d of the leader pin main body 5 are inserted. Also, there is formed an insertion guide portion 21 extending linearly from the pin housing recess 45 toward the tape leader opening 10.
A pin retaining member 50, for detachably retaining the tape leader pin P in the pin housing recess 45, is formed from a plate spring member having a hairpin-shaped cross section. The pin retaining member 50 has an attaching plate portion 50a which extends vertically between the upper and lower cases. The attaching plate portion 50a is clamped between (1) bosses 41 provided on the bottom surface of the top wall of the upper case and the top surface of the bottom wall of the lower case 3 along the inside surface of the case side wall 3b, and (2) the side wall 3b. The pin retaining member 50 further has a pair of upper and lower elastic arm portions 50b which extend from the upper and lower ends of the proximal portion 50d of the attaching portion 50a toward the tape leader opening 10. The outer end portions of the upper and lower elastic arm portions 50b are formed into pin retaining portions 50c, which abut the outer peripheral surfaces of the upper and lower flange portions 5d of the leader pin main body 5.
On the other hand, the pin housing recess 45 of the cartridge case 4 has an abutting surface in the form of a circular arc which receives the outer peripheral surface of the flange portion 5d of the leader pin main body 5. However, the right side portion, on the side of the pin retaining member 50, of the abutting surface has been removed in order to assure installation space for the elastic arm portions 50b and pin retaining portions 50c of the pin retaining member 50.
The tape leader pin P retained in the pin housing recess 45 is pulled out of the cartridge case 4 by a pin catching member 80, called a leader block, which is provided on the side of a recording-reproducing unit. The pin catching member 80 has an engagement cutout 80a which engage with the upper and lower small-diameter portions 5c (see FIG. 1) of the leader pin main body 5. When the engaging operation is performed, the pin catching member 80 first moves linearly in the direction of arrow A toward the tape leader opening 10 and enters the tape leader opening 10 through a side opposite to the case side wall 3b with respect to the tape leader pin P. Then, the outer end of the pin catching member 80 rotates in the direction of arrow B toward the tape leader pin P. The engagement cutout 80a of the pin catching member 80 is caught on the small-diameter portion 5c of the tape leader pin P and is moved back in the direction of arrow C. As a result, the tape leader pin P is pulled out of the cartridge case 4 through the tape leader opening 10. In this manner, the mechanism of the recording-reproducing unit is simplified.
On the other hand, when the magnetic tape cartridge is taken out from the recording-reproducing unit, the pin catching member 80 holding the tape leader pin P advances linearly toward the tape leader opening 10 in the direction opposite to the direction of arrow C. After the tape leader pin P has been retained in the pin housing recess 45, the pin catching member 80 is returned via the tape leader opening 10 along the reverse route of the aforementioned route.
In the tape leader pin P of FIG. 1, incidentally, there is a possibility that the tape leader pin P will be disengaged from the magnetic tape T because of insufficient clamping force, since the coefficient of friction between the magnetic tape T and the pin main body 5 (or the clamp member 6) is low. More specifically, in order to reduce the sliding friction between the magnetic tape T and the magnetic head, a lubricating agent is often coated on the magnetic layer or top surface of the magnetic tape T so that the coefficient of friction is reduced. Similarly, a lubricating agent is coated on the bottom surface of the magnetic tape T. In that case, the coefficient of friction between the pin main body 5 (or the clamp member 6) formed from stainless steel and the magnetic tape T varies with the type of the magnetic tape T. When this coefficient of friction is small, there are cases where the clamping force by the insertion of the clamp member 6 onto the tape leader pin P is reduced.
In addition, when the tape leader pin P is held and pulled out of the tape leader opening 10 of the cartridge case 4 by the pin catching member 80, as described above, the pin catching member 80 is inserted into the tape leader opening 10 in the direction of arrow A and is then rotated in the direction of arrow B to catch the tape leader pin P. For this reason, there is a problem that engagement between the pin catching member 80 and the tape leader pin P cannot be reliably performed, because the tape leader pin P is pushed and moved by the pin catching member 80 when the pin catching member 80 rotates in the direction of arrow B and engages the tape leader pin P.
That is, when the pin catching member 80 rotates in the direction of arrow B and engages the tape leader pin P, there are cases where force is exerted on the tape leader pin P in the direction of arrow B by the pin catching member 80. In such a case, since the right side portion of the abutting surface of the housing recess 45 has been removed, the spring force of the pin retaining member 50 cannot resist the rightward force exerted on the tape leader pin P and therefore the tape leader pin P will be moved out of the pin housing recess 45 or will tilt. As a result, there is a fear that the pin catching member 80 cannot engage the tape leader pin P correctly and the loading operation will not be performed with reliability.
Hence, it has been proposed to provide an abutting portion on a side near the pin retaining member to receive the flange portion 5d of the tape leader pin P and regulate movement of the tape leader pin P during engagement. However, in that case, space for installing the pin retaining member is narrowed, so it becomes difficult to install the hairpin-shaped pin retaining member 50 equipped with the long elastic arm portion 50b. 
To solve this problem, a pin retaining member with a relatively short elastic arm portion can be employed. In that case, if the retaining portion of the outer end of the elastic arm portion of the pin retaining member is forcibly pushed by the tape leader pin P when the tape leader pin P is inserted into the pin housing recess 45 during the unloading operation, there is another problem that plastic deformation will occur near the boundary portion between the attaching portion and short elastic arm portion of the pin retaining member and therefore the short elastic arm portion will no longer return to the original position.
Furthermore, as described in the aforementioned Japanese Unexamined Patent Publication No. 11(1999)-232826, there is a magnetic tape cartridge having separate pin retaining members. The pin retaining members are respectively equipped with elastic arm portions and are independently installed in the upper and lower cases. However, the elastic arm portions of the pin retaining members are equipped at their outer ends with angled pin-retaining portions for retaining the flange portions 5d of the pin leader pin P, and the upper and lower elastic arm portions and pin retaining portions are approximately the same in shape. Because of this, the upper and lower pin retaining members are approximately the same in spring characteristic.
Therefore, when the tape leader pin P is returned into the cartridge case by a pin catching member provided on a drive unit, the upper and lower flange portions 5d of the tape leader pin P are brought into contact with the pin retaining portions of the pin retaining members at approximately the same time and are subjected to approximately the same elastic force. Because of this, the tape leader pin P will be caught on the pin retaining portions and therefore smooth engagement between the tap leader pin P and the pin retaining members will be disturbed.